1. Field of the Invention
The present invention relates to an optical sheet, an electric-field-controlled panel having an optical sheet, a lighting apparatus having an electric-field-controlled panel, a liquid crystal display having a lighting apparatus, and a method of manufacturing an optical sheet.
2. Description of the Related Art
In recent years, liquid crystal displays have come into use in various products such as notebook personal computers (PCs), monitors, car navigation systems, function calculators, small- and medium-size TV sets, large-size TV sets, cellular telephones, electronic pocket diaries, personal digital assistants (PDAs), and the like. Of these products, electronic pocket diaries, PDAs, cellular telephones, tablet PCs, and notebook PCs are frequently used, because the liquid crystal displays mounted on them are small, thin and light. Further, liquid crystal displays are widely used at points-of-purchases (POPs) apparatuses and automated teller machines (ATMs). Still further, liquid crystal displays are used in public-service apparatuses such as ticket machines.
In some cases, the information displayed on any product mentioned above should be concealed from people other than the user of the product. For example, a cellular telephone, a PDA or a tablet PC may display private information while used in public. In this case, the display on the apparatus should better have a small angle of visibility. However, two or more people need to observe the information in some cases. In view of this, the angle of visibility should be controlled and portable apparatuses and public-use information terminals should have a function of controlling the angle of visibility.
In recent years, a removable louver sheet has been used as means for controlling the angle of visibility of the liquid crystal display or the cathode-ray tube (CRT), as is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2003-58066. Further, a system has been put to practical use, in which the liquid crystal display used has no polarizing plates on the front. The user can observe the information only if he or she wears polarizing glasses.
The conventional louver sheet has a light-shielding layer that is several millimeters thick in the direction normal to the sheet, in order to reduce the angle of visibility as much as possible. Any liquid crystal display that uses the conventional louver sheet inevitably has low transmittance and, hence, low luminance. Further, the method of manufacturing the louver sheet is complicated, increasing the manufacturing cost of the louver sheet. Still further, it takes much time and labor to attach and removed the louver sheet to and from the liquid crystal display. With the system wherein the user wears the polarizing glasses, any person other than the user cannot see the information at all.